Stucco (Portland cement plaster) is sometimes removed from a building to determine if proper flashing was installed, replace leaky windows, repair water damaged wood framing members or other reasons that would require the removal of the stucco around windows. It is possible to patch and restore the stucco membrane. Removal procedures can vary depending on the substrate, framing and overall remediation plans. The following outlined procedure is for removal and replacement of cement stucco around windows on wood framed walls. This guide is limited to the removal and replacement of the stucco and not specific to window installation and related flashings. There are several types and styles of windows and a variety of methods for flashing. This document is intended to focus on the lath and cement plaster work for remediation.
It is important to determine the expectations of the building owner and inform them of the finishing options. The finishing options to the repairs around windows depending on the degree or desire of finish appearance and should be discussed prior to the start of work. The following will help with some decisions, options and help clear up confusion for all parties involved.
A comprehensive evaluation of the exterior plaster should be conducted by qualified persons prior to making any decisions for final scope of repairs. An important item needed to determine the full scope of stucco repairs is the type of finish coat (acrylic or cement) on the building and the overall condition of the walls. Has the building been painted and what type of paint was used? Buildings with elastomeric type paints will limit the options of repairs.
Stucco removal can be very dusty protective clothing, eye protection, and a respirator are always recommended. The removal of stucco is best done by cutting the stucco with a power saw using a masonry blade. The blade should be set to just shy of the full thickness of the stucco membrane, usually 3/4 of an inch. This will protect the underlying weather-resistive (WR) membrane from damage. Masonry blades wear down quickly and it will be necessary to adjust the blade depth frequently. The stucco cuts should be approximately 12 to 24 inches away from the window frame. Vertical cuts may be further away from the window as they should reach the next framing member (stud). Once the saw cuts are complete, a cold chisel can be placed into the saw cut and used to break or fracture the last remaining uncut thickness of plaster. The stucco can then be pulled off the wall with minimal damage to the underlying WR membrane. For large areas of removal, it is suggested to cut the stucco into squares that can be easily handled.
In some rare cases the WR membrane may be adhered to the back of the stucco. In these instances it will be necessary to remove the stucco back to point where the stucco is not bonded the WR membrane.
The cut stucco edge will be straight and smooth, it is recommended the edges be jagged and rough. This will produce a better key (bond) between the new patch and existing stucco and can minimize the chance for a separation crack. A hammer can be used to chip away small sections, leaving some of the metal lath exposed if possible.